Winston Churchill has a quote: "If you're going through hell, keep going." It's a guaranteed way to fire up an entrepreneur during times of struggle, but what about the flip side? If you're going through hell, how do you know that it's time to follow the arrows towards the exit sign?

According to the Small Business Association, over 99 percent of all businesses in the U.S. are considered small, which is defined by having fewer than 500 employees. In a study conducted by the Bureau of Labor Statistics, "A business that started in 2004 had a 78.9 percent chance of surviving one year and a 48.4 percent chance of surviving 5 years."

How did those early drop offs know that it was time? Would they have made it if they tried harder, believed a little more, or had a smidge more perseverance? What would Winston Churchill have told a company that was receiving a streak of skeptical venture capitalists vs. a business that really didn't have a market?

At the end of the day, the story you design for yourself (to quit or not to quit) is a call only you can make. Sometimes the outside world has it right - critical comments against your product can mean that it's not a good fit - but sometimes, they have it completely wrong if you haven't found the right people to market to. On the flip side, a few decades ago, a non-profitable business seemed unsustainable. These days, being non-profitable with high user growth rate can land you a billion-dollar valuation.

Whether it's a business you're managing or a job that you're on the fence about, the one thing to ask yourself is this:

Does this make me happy?

It doesn't have to be 100 percent complete happiness all day every day, but it has to be the resounding foundation of what you're doing. It's normal to have bad days, but if the mission of what you're doing doesn't make you want to tell everyone about your project, then it's time to find something that does.

When you're happy with what you're doing, you put everything you have into it. The chances for success increase tenfold. When you're dragging your feet about pitching your product, everyone can see right through you.

Revisiting your happiness factor will help you save a lot of time and heartbreak, and if you're thinking of pulling the plug, know that it's okay. There is something out there that will make your heart shine. If you've made it this far and know that this is what you're meant to be doing, then, keep on keeping on. Churchill would be proud either way.